4 pin is vcc, gnd, gdn, 5 volt. I just left the 4 pins there to line up the board on both sides.

A curious thing with my arduino board is the pins on the signal side aren't consistant with the holes on my project board. There is a little break between 7 and 8 but not enough to be a full row of holes. Had to cut the board and file a small amount to line up the little bit of board.

The other side of gnd and power has a break also but the break is a full width of holes so it is ok.

Can't figure that one out.

Both boards will fit in the forearm, in front of the servo bed and all 6 servos can be unplugged without dissasembling anything and the only wire leaving the arm is the usb for the arduino.

My new printed pulleys are working out great. 25mm diameter by 8mm high with a recess of 4mm deep by 2mm wide.